Generally you will consume more power than one motor doing all the work, and less than two motors sharing the load. The best use of 2WD is starting off the line and hill-climbing. The least benefit is when cruising on level ground; often one motor just tags along and lets the other take the load – or they go into contention
if the two wheels and controllers are set identical. To prevent contention on my ebike, I deliberately set each wheel to a different physical size, and overtly set the power-levels different as well which worked out pretty dang well.
If you are looking to gain efficiency – this is not the thread for you. The fact is that 2WD can and does provide about twice the torque to the ground over a single motor at the same power; two motors individually set to X-wattage will push roughly twice as fast as a single motor set to X-wattage. Another way to look at it: 2WD will get off the line and climb hills faster and cooler than a single-wheel at twice the power; two motors using a total of X-wattage will outperform (though at an economic price) a single motor at the same X-wattage. The downside to 2WD is that you have twice the weight and twice the freewheel drag, but then you get twice the regen braking.
There is no free lunch: 2WD will use more power than a single-wheel drive.
It’s also a heck of a lot of fun! KF
I'm not particualy interested in overall power consumption, not going to be hyper-mile'ing and if I need more range, I'll add more Lipo. My reference to efficiency was in regards to being able to climb a formidable hill @ more than 5-8 mph and not self-destruct a single mini motor. Yes, there have been claims of increased efficiency running two SMALL motors[one rider claiming incredible gains], but until I can explore that myself I tend to dismiss them. It seems clear from real-world 2WD users[of which you are the King], that there will be a loss in efficiency.
But almost all of these discussions[including yours]are from the POV of using two POWERFULL motors.
Real world reports of two small motor set-ups are more rare, Garykard and Chinaphil come to mind. There is evidence that running two small motors all the time may not extract a major penality[as a side note, it would seem that both Chinaphil and Garykard have moved on to Mac rear drives. This should probably tell me something
Aside from the LARGE and SMALL motor 2WD catogories, there can be futher sub-divisions as described by John in CR,
"For the mountains and going slow I'd use identical lower speed wind motors that they call the torque model.....The reason I'd say identical motors is the high stress of steep climbs. You want to share that load equally. For street riding a difference in torque for the two motors could make sense, and that's the route I'm considering with less torque but higher speed capability of the front motor. My goal is different though, and I'm after maximum acceleration and speed while not so much on the front that the wheel spins. That route I get a large wheel on front, which I prefer at the speeds I ride, and the front motor will always be assisting the rear. I will have to dial in the current settings, so the front doesn't get stressed and overheat from carrying too much of the load.".
So what we have here is one approach where the two motors/controllers are the same[in this discussion, I am assuming one battery, as there would appear to be no benefit to using two]and the goal is to raise the performance levels within the parameters of the single motor envelope. The exception here, and this might be considered in the realm of increased efficiency, would be the ability of two small motors to help "pull" each other slightly higher into the zone between power/load and no-load speed. Reports of two small motors vs. one seem to bear this out. For a mini motor user, increasing top speed from say, 21-23 mph to 23-24 mph without raising the voltage is deffinately a big deal.
The second approach attempts to expand the parameters by over-lapping winds, types, controllers, etc.
Since I am seeking a light duty trail bike[more like trials actually] and have no desire to be able to exceed 23-24 mph[Tucson has a wonderful network of bike trails/lanes, but it also has an enforced bicycle speed limit of 20 mph], I am interested in the first approach. And it just seems more elegant to me.
"To run 2 motors, you need two controllers, one throttle and one battery. It's best to combine 2 identical controllers to make sure both will have the same understanding of throttle signal. The same applies to motors, but sometimes a motor you like is not available for front and rear, so then you have to match 2 motors that will have same or very similar no load speed, and play with the simulator to make sure the motors will pull together well."
He, as well as others[Neptronix in particular]go on to say[and I am paraphasing], for a street machine, up to speeds that a mid-sized gear motor can achieve on moderate voltage, one is better off just using a rear Mac/Puma/BMC or BPM. Very effective, less complicated and in the case of the BPM, less expensive. Heck, for the serious off-roader this probably would be a better approach, as it would keep the frt. end light, enabling the rider to loft over trail obstacles. I rode dirt bikes for over 40 years and I understand this well, but I am at the point in life where I would be more inclined to stop, get off, and carry the bike over something like a log.
So now we come full circle and get back to the questions of how to do a 2WD mini-motor rig.
As I mentioned in an earlier post, I think one of the advantages to using low-powered motors is the freedom from worry about applying frt. to rear power differential. Sure, I can get my frt. mounted MXUS to spin on dry pavement, but I have to try and do so. And a spinning frt. tire is easier to control than a rear.
For a purely street ride, I would be inclined to simply run both controllers off one throttle[no mechanical hash-ups are needed]with one switch to drop one motor out of the loop if so desired. Or better yet, one throttle into a Cycle Analyst as Justin has described and one of the two out switched. Which motor to run at say, 80% cruise? Not sure, since I will be using two slightly different motors some experimentation would be required[the fun begins].
For off-road, i think two throttles would provide max. giggles. I already use a trigger left-mounted so it is a "pusher', so it seems to me that adding a right-hand half twist would be the most intuitive set-up. They both require a "forward" motion.
Combining these two approaches would obviously require some creative switching networks, even more fun